1. Field of the Invention
The invention relates to injection molding, and particularly to a mold gate insert and mold gate insert retainer in an injection molding apparatus.
2. Background of the Invention
Injection molding is a common manufacturing practice. Various articles of commercial value such as plastic bottles, toothbrushes, and children's toys, are made using well-known injection molding techniques. Injection molding generally involves melting a material, which is often plastic, then forcing the melt stream at high temperatures and pressures through one or more gates into a mold cavity. The melt cools in the shape of the mold cavity, which is opened to eject the finished part.
The melt is supplied from a machine nozzle, injected into a heated manifold and distributed to the mold cavities through heated nozzles. The heated nozzles are seated within bores in a mold plate that forms the mold cavities. The mold plate is cooled so that melt injected into the cavities can be adequately cooled prior to ejection. However, because the nozzle is heated and the mold plate is cooled, heat from the nozzle is drawn from the nozzle into the mold plate, which can create difficulty in maintaining the melt at an optimum temperature in the nozzle. As a result, it is often desirable to configure the injection molding system to reduce heat transfer from the nozzles to the mold plate, especially proximal to the mold gates, while still maintaining an adequate seal between each nozzle and a respective mold gate.
Front-gated nozzles often include a two piece nozzle seal, including an inner piece and an outer piece, to maintain the position of the nozzle in the mold plate and to provide a seal between the nozzle and the mold plate. In some systems, the nozzle seal suspends the nozzle body within a bore in the mold plate so that there is no direct contact between the nozzle body and mold plate. To further reduce heat transfer between the nozzle and the mold plate, the inner piece generally does not contact the mold plate, and the outer piece which contacts the mold plate, is constructed from materials that are less thermally conductive than the nozzle body or the mold plate. During mold cycles, the temperature of the injection molding system components fluctuate, resulting in thermal expansion and contraction of those components. During the temperature cycles, sealing between the nozzle and the mold gate can be maintained by sliding contact between the outer piece of the nozzle seal and the mold plate.
The conventional two piece nozzle seal is generally threadably secured to the nozzle. In some circumstances, one of the pieces (generally the outer piece) of the nozzle seal may form a portion of the surface of the mold cavity. In an application where the mold cavity surface is angled, the surface of the nozzle seal must be angled to correspond to the angled mold cavity surface. However, because the nozzle seal is generally threaded to the nozzle, the position of the thread starts and stops on both the nozzle and the seal, as well as the act of torqueing the seal, does not permit predictability and repetition of the final angular position of the seal. Thus, the seal's angular orientation cannot be repeated if the seal has to be removed for any reason.
Some conventional ways of avoiding this problem are either to avoid cutting the bottom of the seal or to mark the seal and the nozzle with a scribe line when they are together. When the components are re-installed, the toolmaker must torque the seal until the scribe lines are aligned.
There is therefore a need to provide a more convenient way to seal the gap between the nozzle and the mold gate and to permit easy removal and replacement of the components.